Air-space insulated conductor



April 16, 1940. T. LEHNE Er AL AIR-SPACE INSULATED CONDUCTOR Filed March 18, 1958 Patented Apr. 16, i940 UNITED STATES PATENT OFFICE llavellanil.' Konrad Schluckebier. Berlin-Sieneustadt, Pall Thomas, Berlin-Wilmers-` and Bans Wassmamdorfl, Berlin- Snlndall, Gm, assignors to Siemens Halal/e Aktiengesellschaft, Siemensstadt, near Berlin, Germany, a corporation of Germany Application March 18, 1938, SerialNo. 196,064

A In Germany April z8, 1038 1 claim (C1. 11s-za) This invention relates to air-space insulated conductors having at least one spacer consisting of resistant insulating material and wound in open helical turns around the conductor and a screen or outer conductor arranged over the air-space insulation, and has for its object to attain a very small capacity and therefore a low line attenuation.

In order to form the air-space insulation in l0 the case oi' air-space insulated conductors it has hitherto been customary to wind one or more continuous spacers ilrmly. around the conductor so as to ensure with the aid of the spacers also an accurate centering of the conductor within '5 the sleeve surrounding the same. In such airspace insulated conductors the capacity is the smaller, the greater the pitch of the spacers wound around the conductor. However. the capacity may also be reduced by employing 0 spacers in the form of multiple cores. helices and the like.

According to the invention the capacity of airspace insulated conductors. having at least one spacer consisting of mechanically resistant in- 2li sulating material-i. e. solid insulating material which retains its form and resists compressionwound in open helical turns around the conductor and a screen or an outer conductor or conducting sheath. is reduced to a further extent 3 by rendering self-supporting each cylindrical spacer winding wound around the conductor in spaced relation thereto and by making the inner diameter of the spacer winding at least 50% greater than the outside diameter of the conductor.

The self-supporting spacer winding is obtained in the manner that the spacer is made of mechanically resistant insulating substances and by the fact that a sufilciently small pitch is chosen for the spacer wound around the conductor. By

correspondingly dimensioning the spacer winding.. the latter may be made without dimculties suiiiciently resistant to compression for all operating conditions. Since the spacer winding is so designed as to be self-supporting the sir-space insulation designed according to the invention presents a relatively high resistance to mechanical stresses. 'I'he loose arrangement of the conductor within the spacer winding has from a mechanical point oi' view thefurther advantage that the conductor is sumciently free to move in the case of longitudinal changes caused by the fluctuations of temperature without the spacer. The lextremely small capacity is obtained by the-fact that the spacer winding just touches the conductor at intervals. 'I'he distance of the points at which the spacer winding comes into contact with the conductor may be still increased by slightly corrugating the conductor, not enough, however, to I impair the electric properties of t. The eccentricity of the inner conductor present at certain spaced pointsin the case of the airspace insulation according to the invention is practically without any importance, since over l0 the air-space insulation is arranged a screen or return conductor by means of which the conditions of capacity are dened to a great extent.

It is also possible according to the invention to build up the air-space insulation of the conu ductor of a plurality, preferably of two spacer layers, only the inner spacer layer being designed according to the invention. 'Ihls has the advantage that the inner spacer winding may be made of a` relatively thin thread so that on the .o one hand the manufacture of the air-space insulated conductor is facilitated and on the other hand the capacity thereof is rendered smaller.

Cellulose derivatives or. suitable insulating substances of the group of the polyvinyl compounds, for instance, polystyrene are preferably employed as mechanically resistant insulating substances for the spacer windings. In case the air-space insulated conductor is employed in high-frequency cables the use of flexible polystyrene threads is l0 preferable which are rendered flexible in the plastic state of the material by suitable well-known stretching methods.

If the air-space insulated conductor is to be used as a highly flexible conductor the protective 85 sleevesY arranged over the self-supporting airspace insulation are designed in the form of highly flexible sleeves. Highly flexible screens in the form of metallic foil windings, wire meshes, etc., and furthermore coverings of fibrous mate- 40 rials are employed for this purpose. A preferable form of the invention consists in manufacturing the protective sleeve arranged over the screen or outer conductor from rubber or rubberlike artificial substances and in metallizing the same preferably with pulverized aluminum. It may also be advantageous to arrange one or more insulating and in some cases water-proof protective layers not only over the screen but also underneath the same. Such highly exible eonductors are employed to advantage as downleads for aerial systems.

In the accompanying drawing are diagrammatically shown various forms of the invention.

In these drawings- Fig. 1 represents a high-frequency concentric air spaced cable having one spacer thread of solid insulating material wound around the inner conductor.

Fig. 2 represents a similar cable.' in which around the spacer thread an additional thinner spacer thread is wound.

Fig. 3 represents a cable in which the entire-air space insulation is divided into two Separate spacer layers.

Fig. 4 represents a cable with a relatively thin inner conductor. a self-supporting spacer winding of large diameter, and a braided outer conductor.

Fig. 5 represents a cable similar to that o! Fig. 4, having a double spacer winding placed around the inner conductor, and

Figs. 6 and 7 show an insulation sleeve arranged between the air spacing helix and the braided outer conductor.

Fig. l shows a concentric high-frequency cable according to the invention. Around the inner conductor ||l is wound in open helical turns the solid thread of circular cross-section consisting of resistant insulating materials, for instance, of polystyrene; however, in contradistinction to the known types of inner conductors in such a manner as to obtain by selecting a small pitch a self-supporting spacer winding which is resistant to compression within certain limits and whose inner diameter is by more than 50% greater than the diameter of the conductor Il. The spacer winding is surrounded by a closed band winding I2 of insulating material. The outer conductor 3 consisting of good conducting band segments, the open band winding I4, the closed band winding |5 of insulating material and the water-tight cable sheath |5 are arranged successively around the closed band winding l2. Since the thread used for the spacer winding should not exceed a predetermined thickness this type of air-space insulation is particularly employed in concentric cables of very small cross-section; i. e., in cables with relatively great line attenuation.

According to Fig. 2, the spacer 2|, consisting of a centrally arranged thread 22 and of the thread 23 wound around the latter in open helical turns, is wound around the inner conductor 20 in open helical turns. The spacer 2| is wound as an open spacer Winding in a manner so as to be self-supporting, and is so spaced from the conductor 2|! that the inner diameter o! the spacer winding 2| is at least 50% greater than the diameter of the conductor 20. 'I'he threads 22 and 23 consist preferably of polystyrene. The thread 22 may be a single or a multiple thread; for instance, a cord consisting oi' several thin strands. 'Ihe closed band Winding 24 of insulating material, the return conductor 25 consisting of good conducting band segments, the open band winding 26 serving to hold together the outer conductor bands, the closed band winding 21 of insulating material and the water-prooi cable sheath 28 are arranged in respective succession over the spacer winding 2|.

Fig. 3 shows an embodiment in which the entire air-space insulation of the conductor is subdivided into two spacer layers. Around the inner conductor 30 is first wound the spacer winding 3| consisting oi.' a thread and whose inner diameter is according to the invention greater than that of the conductor. By the use of suitable insulating material and by suitably dimensioning the. spacer winding the -latter becomes self-supporting and suillciently resistant to compression so that further layers of insulation may be arranged around the spacer winding. According to the embodimentshown in Fig. 3 a closed band winding I2 consisting of insulating material is ilrst wound around the spacer winding Il. The secondspacer layer ls formed of the spacer u wound in open helical turns over which is arranged a closed band winding Il of insulating material. Whenusing the cable for high-frequency n the spacers 3| and 3l as well as the band windings 32 and Il are preferably made of high-grade insulating material suitable tor high-frequency such as, for instance, polystyrene. The spacer in the present case is made in the form of a cord consisting oi such insulating material; however, it may also be made in another known manner; for instance, in the form of a thread helix consisting of mechanically resistant insulating material. Over the band winding Il are arranged nrst the outer conductor 35, then the open band winding 30, the closed band winding 31 of insulating material and lastly the water-prooi cable sheath 38.

Figs. 4 to 7 show further embodiments of the invention which are employed i'or exible airspace insulated conductors, for instance, for aerials.

According to Fig. 4 the relatively thin conductor 4l is surrounded with the self-supporting spacer winding 4| made of mechanically resistant insulating materials and whose inner diameter is preferably many times greater than the diameter of the conductor. Ebonite, derivatives of cellulose or polymers of the group of the polyvinyl compounds, such as, for instance, ilexible polystyrene are preferably employed as mechanicallyV resistant insulating materials for the spacer winding. Directly over the spacer winding 4| is arranged. the screen or return conductor 42 designed in the form of a wire braid. The sheath I3 of insulating material which consists preferably of rubber or of any other suitable artificial material, for instance, of mixed polymers oi' vinyl chloride and ester of acrylic acid, serves as an outer protection. 'I'he closed sheath of insulating material may be metallized, for instance, with pulverized aluminum. In this manner the conductor is provided with a surtace having a metallic luster so that in the event of rays oi light striking the conductor the same are easily reiiected and therefore cannot unfavorabLv atleet the protective sheath.

Fig. 5 shows another embodiment in which the conductor is surrounded with two self-supporting spacer windings arranged one over the other. 50 is the conductor around which are wound the two spacer windings 5| and 52. The latter may in some cases be made oi dierent insulating materials; i'or instance, the spacer winding 5| of polystyrene or the like and the spacer winding 52 of ebonite or the like. Over the spacer winding 52 are arranged in succession the metallic screen or outer conductor 53, a ilber covering 54 and a layer oi varnish 55. for instance, aluminum varnish.

According to the embodiments shown in Figs. 6 and 'I an insulation sleeve is also arranged between the air-space insulation and the screen. In both figures the same parts are denoted by similar reference characters. The inner conductor may either be made of tinned or zinc-coated steel wire or of aluminum wire so that the use of a copper wire is not absolutely necessary. A helix 52 of artiilcial substance, for instance, oi' polystyrene (particularly in a stretched state) momie surrounds the conductor il in spaced relation thereto. 'I'he helix may be designed in such a manner as to be stretched to a greater or smaller extent than is shown in the drawing. Around the helix is arranged a sheath of artificial substance either in the form of a closed sleeve 03 as shown in Fig. 6 or a sleeve formed by a band winding 0l as shown in Fig. '7. As material for the sleeve 6I particularly an artificial substance' is employed capable of being sprayed, for instance, consisting oi mixed polymers of vinyl compounds or of other hydrocarbons, whereas in the case of the sleeve M an artificial substance is employed capable of being worked into a ribbon or foll and consisting, for instance, of ce1- lulose derivates repelling water or aiterchlorinated polyvinyl chlorides or the like. Over this sleeve Il or 84 is arranged a more or less finemeshed metal covering B5 which may consist of the same materials as those already mentioned for the inner conductor. As an outer covering a closed sheath 66 of artificial substance as in Fig. 6 or a sheath 61 of textile fabric as in Fig. 7 may be arranged over the metal covering 05, which textile fabric may consist of one or more layers of artificial materials or artificial iibrous materials and which is particularly to be varnished. The purpose of this sheath 80 or 61 is to protect the conductor as a whole against attacks by oils. operating or motive fluids and the like or against corrosion. It is also possible to use structural parts of the one embodiment in the other embodiment; for instance. to interchange the sheaths I3 and M with one another. Also other dimensions may be used instead of those shown; for instance, the sleeve il may consist of several windings whose lap Joints are displaced with respect to one another.

The figures show the invention as applied to high-frequency cables with a single concentric or screened conductor. The invention may obviously also be applied to high-frequency cables with several concentric or screened conductors.

What is claimed is:

1. An air-space insulated cable, including in combination a conducting sheath, a conductor within said sheath, and at least one open-wound self-supporting spacing helix, formed by a strand element of insulating material, surrounding the inner conductor and disposed within lsaid conducting sheath, the inner diameter of said helix being at least 50% greater than the diameter of said inner conductor. and the latter being disposed in the helix to have freedom of movement therein.

2. An air-space insulated cable, including in combination a conducting sheath. a conductor within said sheath, and at least one open-wound spacing helix formed of a strand element, said helix surrounding the inner conductor and disposed within said conducting sheath, said strand element consisting of a solid, mechanically resistive insulating material to render said helix self-supporting, the inner diameter of said helix being at least 50% greater than the diameter of said inner conductor, and the latter being disposedinthehelixtohavefreedomofmovement therein.

8. An air-space insulated cable, including in 4. An air-space insulated cable, including in combination a conducting sheath, a conductor within said sheath, an open-wound self-supporting helix consisting of an insulating material strand element and surrounding the inner conductor and disposed within said conducting sheath, the inner diameter of said helix being at least 50% greater than the diameter of said inner conductor, and the latter being disposed in the helix to have freedom of movement therein, a second strand element of insulating material wound in an open helix around the first helix and suitably spaced therefrom, and a closed band winding of insulating material disposed between said two helical windings.

5. An air-space insulated cable, including in combination a conducting sheath, a conductor within said sheath, and at least one open-wound self-supporting spacing helix, formed by a strand element of insulating material, surrounding the inner conductor and disposed within said conducting sheath, the inner diameter of said helix being several times greater than the diameter of said inner conductor, and the latter being disposed in the helix' to have freedom ox' movement therein, said insulating material consisting of a flexible polyvinyl compound.

6. An air-space insulated cable including in combination a highly flexible conducting sheath, a conductor within said sheath, and at least one open-wound self-supporting spacing helix, formed by a strand element of insulating material, surrounding the inner conductosl and disposed withln said conducting sheath, the inner diameter of said helix being several times greater than the diameter of said inner conductor, and the latter being disposed in the helix to" have freedom of movement therein.

7. An air-space insulated cable, including in combination a highly flexible conducting sheath. a conductor within said sheath, and at least one open-wound self-supporting spacing helix, formed by a strand element of insulating material, surrounding the inner conductor and disposed within said conducting sheath, the inner diameter of said helix being at least 50% greater than the diameter of said inner conductor, and the latter being disposed in the helix to have freedom of movement therein, and a highly iiexible closed sheath of insulating material disposed between said conducting sheath and said spacing helix.

HANS WASSMANSDORFF.

KONRAD SCHLUCKEBIER. PAUL THOMAS. TIEODOR LEHNE. 

